Software defined networks (SDNs) enable network programmability to support multi-vendor, multi-technology, multi-layer communications. Recently, efforts have been made to integrate optical transport within an IP/Ethernet-based SDN architecture to leverage optical transmission benefits such as low interference, long reach, and high capacity transmission with lower power consumption. Such networks are referred to as transport SDNs (T-SDNs). T-SDNs can be realized by enabling flexibility and programmability in transmission and switching network elements, such as transponders and reconfigurable optical add-drop multiplexers (ROADMs), management of optical channels such as by flexible-grid channel mapping, and extracting control plane intelligence from physical hardware to the centralized controller.
Recent efforts toward enabling flexibility and programmability in optical transponders have produced transponders with flexible modulation formats. The modulation formats are changed dynamically to meet optical signal-to-noise ratio (OSNR) requirements at receivers. Some optical technologies with flexible channel spacing exist using transponders that generate super-channels. In other cases, transponders with flexible forward error correction (FEC) coding are demonstrated. However, since transponders are not used as store-and-forward network elements, data flow conservation must be observed inside the transponder. Thus, transmission rate at a line interface must be the same as the data rate at a client interface. The rate adaptation flexibility at line interfaces therefore cannot be achieved until and unless the rate at client interfaces can be dynamically adapted.
Existing interfaces use transponders that are connected to multiple low-speed router ports of the same router. Flexible client and line interfaces can be realized by controlling and managing the router ports as a single virtual router port, enabling/disabling such ports in proportion to traffic. Distribution of traffic over multiple Ethernet interfaces of the router ports can be performed using link aggregation groups, which use inverse multiplexing to distribute a large capacity Ethernet payload among multiple parallel channels.
In a multi-flow architecture, a transponder may be connected to a router using a high-speed fixed-Ethernet interface. Inside the transponder, the Ethernet frames are distributed over a number of fixed-rate optical transport unit (OTU) framers proportional to the effective traffic volume using a flow distributor, which distributes Ethernet frames (for example, based on virtual local area network tags) over fixed-rate OTU channels. The optical channels established from the OTU framers form a link aggregation group channel. Thus, the transponder can change the link rate of a line aggregation group channel by adapting the distributions of Ethernet frames over the fixed-rate OTU framers.
However, existing technologies are limited in the granularity at which they can provide flexible client and line interfaces. For example, using LAG and multiple WDM channels as described above, sub-wavelength granularity is not available and an operator has to manage a large number of channels to offer true flexibility, thus increasing the overall complexity and cost for operating the network.
Transponder architectures proposed so far that offer flexibility in the sub-wavelength granularity, for example the so-called multi-flow transponder architectures, make use of a large number of fixed-rate OTU framers and electro-optical modulators, thus leading to increased system cost.
At the same time, most existing commercial transponders do not demonstrate any of the aforementioned flexibility features, which may result to poor spectral efficiency performance for the routing and resource allocation process in networks making use of such transponders.
Moreover, existing transponder technologies do not allow disabling parts of the transponder. As a result, they always operate at the maximum possible data rate, even though the actual data traffic that needs to be carried is less, hence demonstrating poor energy efficiency.